A strange ignition problem

When I first start up my Hailwood Replica, it only runs on one cylinder, the horizontal one. The vertical cylinder only chimes into life if I pull the plug cap off, just enough that the contact in the plug cap is not touching the spark plug terminal. When the engine is up to temperature, I can push the plug cap all the way on, but the engine does not run as cleanly as when the plug cap is partially “off”! Any ideas?

Hello Mikie.
That does sound very odd.
What does the spark look like if you take the plug out and hang it in the lead, is it the same as the horizontal one?
The first thing to do is fit new plugs and make sure that the gap is correct, which is 0.6 mm the plugs should be Bosch W7B, NGK B7HS, or Champion L82C
After that you can swap components, ie coils, resistors and Bosch CDI boxes between the vertical and horizontal cylinders, to see if the fault moves with one on the parts?
Have the ignition pick-ups been changed at all, the insulation on the leads does decay after a few years, as they were never meant to run in hot oil!

I may not even be ignition related but fuel mixture related?


Hi Kevin

Yes it is very strange. I’ve fitted new plugs and the pickups were changed recently. Swapping things over between cylinders seems like a good idea. This seems to defy the laws of physics. To get a spark at the plug tip, it first has to “jump” a gap at the plug cap. A friend of mine says there is a technical term for this behaviour, but I can’t remember what it is! I’ll have to get in touch with him to see if he knows how to cure it!